1. Field of the Invention
The present invention relates to a manufacturing method of a circuit pattern, a thin film transistor (hereinafter, also referred to as a TFT), and an electronic appliance using a droplet discharge method typified by an ink jet method and relates to a manufacturing method of a display device including the thin film transistor. In particular, the present invention relates to a manufacturing method of a circuit pattern such as a wiring, a thin film transistor, and an electronic appliance.
2. Description of the Related Art
In a manufacturing process of a thin film transistor and an electrical circuit including the thin film transistor, various kinds of thin films such as a semiconductor, an insulator, or a conductor are stacked over a substrate. In such a process, photolithography is widely known as a method for forming a pattern. A photolithography is a technique in which a pattern of a circuit or the like, which is called photomask and formed of a material which does not transmit light over a light-transmitting flat surface, is transferred to a predetermined substrate by utilizing light. Photolithography is widely used in a manufacturing process of a semiconductor integrated circuit and the like.
There are two main problems with photolithography. One is that a large amount of resource is consumed. In a conventional manufacturing process of a TFT utilizing photolithography, a number of steps such as light exposure, development, baking, and peeling are required because of a mask pattern called photoresist formed of a photosensitive organic resin material. Therefore, in order to reduce a manufacturing cost in a manufacturing process of a TFT, it is reasonable to take reduction in the number of steps of photolithography into consideration. Further, if it becomes possible to manufacture a TFT without photolithography, significant reduction in the manufacturing cost can be expected.
The other problem has been caused as a size of a mother glass substrate increases. A glass substrate is often used as a substrate for manufacturing a liquid crystal display device, an EL display device, or the like. A mother glass substrate has a size from 300 mm×400 mm of the first generation in the beginning of 1990, to 2160 mm×2400 mm of the eighth generation. A device for the eighth generation is developed and released in 2006. Such increase in size of the substrate generates two main advantages. One is that productivity is significantly improved since a number of panels for a display device can be manufactured with one mother glass substrate. The other is that a large panel can be manufactured. However, a large substrate is difficult to be exposed to light at one time with a light exposure apparatus used for transferring a mask pattern in a photolithography step.
Therefore, as an alternate technique for photolithography, a method of forming a pattern using an ink jet technique is receiving attention. The ink jet technique is originally developed for printing record, since only needed quantity of material can be located on a needed location, application of the ink jet technique to a field relating nanotechnology such as a semiconductor process is considered.
As an approach to nanotechnology, a top-down method and a bottom-up method can be given. The former is a technique in which a minute structure can be manufactured by stacking a material and then etching a desired region thereof. The latter is a technique in which a minute structure can be manufactured by stacking a material in an atom or molecular level. The top-down method has supported the conventional nanotechnology and photolithography is widely used in a manufacturing process of a semiconductor integrated circuit and the like. However, it seems that the limit of the top-down method is being reached. Recently, the bottom-up method draws attention. It can be said that a technology for manufacturing a TFT using an ink jet method is included in the category of the bottom-up method.
As an example of a technique for manufacturing a TFT using an ink jet method, Patent Document 1 can be given (Patent Document 1: Japanese Published Patent Application No. 2005-311325).